Certain textile articles, for example bed sheets, are made from fabrics presenting so-called drawn-in selvedges. Such drawn-in selvedges are obtained during weaving by drawing in, between the warp yarns, the free end of the weft yarn along the selvedge; in this way, the selvedge is clean and the fabric no longer needs to be subsequently cut along the selvedge. However, due to the drawing-in of the weft yarns, the selvedge of the fabric presents an excess thickness and an increase in density of textile material. This local heterogeneity causes differences in behaviour during the treatments undergone by the fabric and in particular during drying of the fabric after impregnation and padding. It has been noted in particular that, at the exit of a drying tenter, there was a considerable difference between the residual humidity rate of the fabric itself and that of the selvedges. Such difference is moreover accentuated when the fabric is transported into the drying tenter by means of a device incorporating clips which grip the fabric along the selvedges on entering the tenter and maintain it to full width until leaving said tenter. The presence of the clips hinders evaporation of the water along the selvedges and does not allow the fabric to dry over a constant transverse humidity profile.
The differences in humidity rate observed between the selvedges and the rest of the flat material, due to the grippers and/or to the drawn-in selvedges, lead the users to overdry the whole of the material in order to obtain an acceptable humidity rate on the selvedges. This practice involves an excess consumption of energy and a limitation of the production rates.
In the domain of drying by a micro-wave radiation, British Pat. No. 1 211 789 discloses a device for drying a glue line along a multi-sheet paper pad. This device comprises an elongated ridged waveguide which is slotted on one of its faces, and guiding means such that the edge of the multi-sheet paper pad containing the glue line can be inserted in the waveguide through the slot and that the glue line is positioned in the region of concentrated energy made by the ridge inside the waveguide.
This known device is not entirely suitable in the case of drying selvedges of a flat, particularly textile, material, since drying is effected locally along a given line defined by the ridge, whilst it is desired to dry the whole surface corresponding to the selvedge.
A device has now been found, and this forms the subject matter of the present invention, whose purpose is specifically to dry a selvedge of a continuously advancing flat material, particularly a textile material, and which is particularly well adapted for pre-drying or post-drying the selvedge of such a material in addition to a conventional drying installation such as a tenter.